A fuel cell is an apparatus that simultaneously generates electric power and heat by electrochemically reacting a fuel gas including hydrogen and an oxidizer gas including oxygen such as air with each other.
The fuel cell is generally configured by stacking plural cells (single cells) on each other and press-fastening the stacked plural cells with a fastening member such as a bolt. Each one of the cells is configured by sandwiching a membrane-electrode assembly using a pair of plate-like electrically conductive separators therebetween. The outer circumferential area of the membrane-electrode assembly is held by a frame to improve its handling performance. The membrane-electrode assembly including the frame will herein be referred to as “electrode-membrane-frame assembly”.
The membrane-electrode assembly includes an electrolyte membrane and a pair of electrode layers formed on both surfaces of the electrolyte membrane. One of the pair of electrode layers is an anode electrode and the other thereof is a cathode electrode. Each of the electrode layers includes a catalyst layer formed on the surface of the electrolyte membrane, and a gas diffusion layer formed on the catalyst layer.
In the fuel cell having the above configuration, a fuel gas is supplied to the anode electrode and, thereby, the fuel gas is converted into protons by the catalyst layer. The protons pass through the electrolyte membrane and reach the catalyst layer of the cathode electrode to bond with the oxidizer gas supplied to the cathode electrode. Thereby, an electric power generation reaction occurs.
The catalyst layer generally includes a catalyst, a catalyst carrier, and an electrolyte. The catalyst produces protons from the fuel gas and causes the protons and the oxidizer gas to bond with each other. The catalyst carrier extracts the electricity generated by the electric power generation reaction from the catalyst to an external circuit. The electrolyte propagates the protons produced from the fuel gas.
The electric power generation performance of the fuel cell is influenced by the reaction efficiency of the catalyst layer, the diffusivity of the gas in each of the gas diffusion layer and the catalyst layer, the resistive loss of the electricity generated by the electric power generation reaction, the proton conductivity, etc. To improve the electric power generation performance of the fuel cell, it is required that such paths are excellently formed as the propagation path for each of the fuel gas and the oxidizer gas, the electricity conduction path for the electricity extracted by the catalyst, and the proton conduction path for the protons produced from the fuel gas.
The protons need to be propagated not only into the inside of the catalyst but also from the catalyst to the electrolyte membrane. Therefore, the proton conduction path needs to be formed for the protons to excellently be propagated also in the vicinity of the interface between the catalyst and the electrolyte membrane.
A method of forming the proton conduction path in the vicinity of the interface between the catalyst layer and the electrolyte layer can be, for example, a method disclosed in Patent Document 1 (Japanese Unexamined Patent Publication No. 2001-325963). FIG. 9 is a schematic explanatory diagram of a manufacture method of a membrane-electrode assembly disclosed in Patent Document 1.
As depicted in FIG. 9 (in its left-hand portion), an electrolyte membrane 101 and a pair of electrode layers 102 are prepared. The electrolyte membrane 101 has a siloxane monomer component 105a mixed therein. The electrode layers 102 each include a catalyst layer 103 and a gas diffusion layer 104. The catalyst layer 103 has a siloxane monomer component 105b mixed therein.
As depicted in FIG. 9 (in its right-hand portion), the pair of electrode layers 102, 102 are disposed such that the catalyst layers 103, 103 are on and in contact with the electrolyte membrane 101 and, thereafter, heat and a pressure are applied to the electrolyte membrane 101 and the catalyst layers 103 to bond these to each other. At this time, the siloxane monomer component 105a and the siloxane monomer component 105b condensation-polymerize with each other and, thereby, siloxane polymers 106a and 106b are formed straddling over the catalyst layers 103 and the electrolyte membrane 101. These siloxane polymers 106a, 106b act as the proton conduction path in the vicinity of the interface between the catalyst layers 103 and the electrolyte membrane 101.
A configuration to form the proton conduction path in the vicinity of the interface between the catalyst layer and the electrolyte membrane can be, for example, a configuration disclosed in Patent Document 2 (Japanese Unexamined Patent Publication No. 2012-64343). FIG. 10 is a schematic explanatory diagram of an outlined configuration of a membrane-electrode assembly disclosed in Patent Document 2. Patent Document 2 discloses the configuration having a porous support 203 disposed therein that penetrates an electrolyte membrane 201 and at least a portion of each of catalyst layers 202.